The present invention is related generally to the field of orthodontics. More particularly, the present invention is related to improved systems and methods for removably attaching a dental positioning appliance to the dental features of a patient during orthodontic treatment.
Orthodontic treatments involve repositioning misaligned teeth and improving bite configurations for improved cosmetic appearance and dental function. Repositioning teeth is accomplished by applying controlled forces to the teeth over an extended period of time. This is conventionally accomplished by wearing what are commonly referred to as “braces.” Braces comprise a variety of appliances such as brackets, bands, archwires, ligatures, and 0-rings. The brackets and bands are bonded to the patient's teeth using a suitable material, such as dental adhesive. Once the adhesive has set, the archwire is attached to the brackets by way of slots in the brackets. The archwire links the brackets together and exerts forces on them to move the teeth over time. Twisted wires or elastomeric 0-rings are commonly used to reinforce attachment of the arch wire to the brackets. Attachment of the arch wire to the brackets is known in the art of orthodontia as “ligation” and wires used in this procedure are called “ligatures.” The elastomeric 0-rings are called “plastics.”
After the archwire is in place, periodic meetings with the orthodontist are required, during which the patient's braces will be adjusted. This involves installing different archwires having different force-inducing properties or by replacing or tightening existing ligatures. Between meetings, the patient may be required to wear supplementary appliances, such as elastic bands or headgear, to supply additional or extraoral forces.
Although conventional braces are effective, they are often a tedious and time consuming process requiring many visits to the orthodontist's office. Moreover, from a patient's perspective, they are unsightly and uncomfortable. Moreover, the archwire and ligatures which connect the brackets in a continuous network make brushing, flossing between the teeth and other dental hygiene procedures difficult, possibly contributing to the development of gingivitis. Consequently, alternative orthodontic treatments are needed. In particular, it would be desirable to use appliances which can be removed by the patient during daily dental hygiene routines, while participating in athletic activities, or for cosmetic purposes.
A particularly promising approach relies on the use of elastic positioning appliances for realigning teeth. Such appliances comprise a thin shell of elastic material that generally conforms to a patient's teeth but is slightly out of alignment with the initial tooth configuration. Placement of the elastic positioner over the teeth applies controlled forces in specific locations to gradually move the teeth into the new configuration. Repetition of this process with successive appliances comprising new configurations eventually moves the teeth through a series of intermediate configurations to a final desired configuration. A full description of an exemplary elastic polymeric positioning appliance is described in U.S. Pat. No. 5,975,893, and in published PCT Publication No. WO 98/58596 which designates the United States and which is assigned to the assignee of the present invention. Both documents are incorporated by reference for all purposes.
In addition to their ease of use, polymeric positioning appliances are generally transparent, providing an improved cosmetic appearance, and impart substantial force on the teeth, due to stiffness of the appliance. The stiffness of an elastic positioning appliance is a result of the modulus of the thermoformable polymer materials from which it is made. The higher the modulus of the materials, the higher the stiffness of the appliance. When a patient positions such an appliance over a prescribed group of teeth, one or more of the teeth will provide a base or attachment region for holding the positioning appliance in place while the stiffness of the polymeric material will impart a resilient repositioning force against one or a portion of the remaining teeth. By designing the appliance to cover the teeth, a much larger contact surface area is afforded compared to traditional spring retainers and wire-based appliances. However, such attaching and repositioning abilities of removable elastic positioning appliances are still dependent on the physical features and configuration of the patient's teeth, palette, and previous dental work, to name a few. For example, shell-like elastic polymeric positioning appliances have difficulty applying certain forces to individual teeth, such as extrusive force (e.g. pulling or raising a tooth relative to the jaw).
Attachment devices anchored to one or several teeth can improve repositioning of the teeth with polymeric appliances. Particularly difficult tooth movements are rotations and extrusions. Using appliances with attachment devices can improve tooth rotation and extrusion. However, during treatment, coupling between an appliance and attachment may become disengaged. This disengagement may occur if a tooth does not move as planned, or moves in a planned direction but not as rapidly as planned. If the planned position of the tooth and attachment differs from the actual position of the tooth and attachment, the receptacle for the attachment formed in the polymeric shell may not properly receive the attachment on the tooth. If the receptacle formed in the polymeric shell does not properly receive the attachment, the force applied to the tooth decreases and the treatment outcome may be less than ideal.
Thus, it would be desirable to provide tooth positioners, systems, and methods which apply adequate force in desired directions to selected teeth at specific times during treatment. In particular, it would be desirable to enable the fabrication and use of removable positioners and systems which can apply extrusive, rotational, and other directional forces which have heretofore been difficult to apply with removable positioners. It would also be desirable to reduce the cost of the orthodontic treatment and retain the patient benefits of a removable appliance in cases where they might not otherwise be available. At least some of these objectives will be met by the designs and methods of the present invention described hereinafter.